Choi, who led by two strokes after two rounds and a single shot after 18 holes, completed 54 holes at 14-under-par 199, one clear of Christina Kim at Highland Meadows Golf Club.
Kim posted a 4-under 67 to move to move to minus-13, while Katherine Hull carded a 6-under 65 to charge into a share of third place at 10-under par 203.
Sharing third place with Hull were Kristy McPherson (67) and Inbee Park (70).
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